In the field of motorcycles, and in particular mopeds, it is known to use, at the front section, an oscillating bar suspension.
In particular, it is a single bar, therefore asymmetric, system consisting of a fork with a single rigid bar, also called steering bar, on which an oscillating bar forms a junction, called pack, facing towards the rear, which ends on the wheel pin.
The steering bar is mechanically linked to the steering wheel of the motorcycle.
Moreover, the shock absorber unit typically consisting of a spring and a shock absorber, is attached on the oscillating bar.
The shock absorber unit mechanically connects the rigid fork with the wheel pin to each other, so that altogether the suspension takes the shape of a parallelogram.
Usually, the shock absorber unit is connected tightly to the wheel pin and to the fork: typically the foot, or lower end of the shock absorber unit, is connected to the wheel pin by a rigid bracket. From a theoretical point of view, the shock absorber unit always works in pure axial compression condition, since the forces exchanged between the wheel and the body are absorbed by the oscillating bar and the single bar fork.
Actually, however, because of the clearances and deformations of the mechanical components, the shock absorber unit does not always work in the theoretical pure axial compression condition but is subject to a bending moment which tends to oppose the sliding between the lining and the stem of the shock absorber unit itself.
The deformations and thus the jamming of the shock absorber unit increase when the connection bracket of the shock absorber unit to the wheel pin is used as an element of support and fixing of the front brake, typically of the disk type. In this case, in fact, the brake transmits considerable strength and torques to the foot which tend to further deform the bracket connecting the foot of the shock absorber unit and thus to lose the straightness and relative coaxiality between the lining and the stem. The result is a difficult sliding of the shock absorber unit and a non-optimal behavior of the front end, further worsened during the braking action.